Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$227.85	11.496%	$254.0436	$254.04	$254.05	$254.00
Purchase #2	$105.60	6.516%	$112.4809	$112.48	$112.50	$112.50
Purchase #3	$61.68	10.150%	$67.9405	$67.94	$67.95	$67.90
Purchase #4	$34.96	13.731%	$39.7604	$39.76	$39.75	$39.80
Purchase #5	$231.63	3.583%	$239.9293	$239.93	$239.95	$239.90
Purchase #6	$203.78	9.322%	$222.7764	$222.78	$222.80	$222.80
Purchase #7	$47.54	11.169%	$52.8497	$52.85	$52.85	$52.80
7 purchase totals =	$913.04		$989.7808	$989.78	$989.85	$989.70